The synthesizer control characters (V, O, T, U and X) always take one integer argument and always affect all the rest of the notes that are played. V stands for Voice and is the key to polyphonic music. Since polyphonic music is achieved by playing notes in different voices, you will use V a lot.
Each note will be played when the previous note is done, but if you switch voices, the next note will be played immediately (if the voice you switch to is free). This will play the C note, followed by E and G at the same time. There are three voices available: 1, 2 and 3.
PLAY "V1 CE V2 G"
This program gives you a nice riff:
10 FOR A=1 TO 4 20 PLAY "V1 CE CV2EV3G" 30 PLAY "V1 CGCC V2EV3G" 40 PLAY "V1CV2EV3G" 50 NEXT